In a hot strip rolling mill or heavy plate rolling mill, steel is rolled. Material properties of the steel are substantially set in a downstream cooling section. For this purpose, a coolant is applied to the steel as the latter passes through the cooling section. This sets the temporal cooling profile of the steel passing through the cooling section. The material properties are also set on account of the temporal profile of the cooling operation.
The cooling profile is generally determined by a temporal temperature profile. Earlier strategies prescribe a distribution of the coolant quantity according to a predefined cooling strategy and a coiling temperature or final cooling temperature (i.e. the temperature of the rolling stock when the latter runs out of the cooling section). In the case of standard steels, this procedure is without problems. However, problems do arise in the case of steels with a high carbon content. This is because the stipulation of a temperature profile is unfavorable owing to the heat of transition which arises during the phase transition from austenite to ferrite and cementite. In many cases, it is even the case that only a final temperature to be reached is predefined in conjunction with a predefined cooling strategy. This type of stipulation can even be ambiguous, i.e. there is more than one solution for the water quantity with which the coiling temperature or the final cooling temperature is reached with a given cooling strategy. The material properties of the steels cooled differently in this way differ entirely, however.
In the case of steels with a high carbon content, fully automated operation is therefore not possible in the prior art. There are difficulties which arise repeatedly in practice when attempting to cool steels with a high carbon content in a fully automated manner. Material which does not have the desired material properties is repeatedly produced. These materials have to be remelted.
In practice, attempts are made to overcome the problems by trying to avoid such materials and stipulations. This reduces the producible spectrum of materials.
EP 1 732 716 B1 discloses an operating method for a cooling section for cooling a rolling stock, in which method the temperature of the rolling stock is detected on the input side of the cooling section. A quantitative coolant profile is determined, such that a rolling stock section, at a predefined point of the cooling section, is at a predetermined temperature and has at least one predetermined phase proportion (for example of austenite).
The above methods ultimately described already represent an improvement to the remaining prior art. However, they still do not work completely satisfactorily.